A variety of studies are underway which involve the opioid peptides as they relate to physiological processes. Included are attempts to study the formation and subsequent metabolism of the materials, their relation to stress, and the ways in which they can be investigated, in terms of receptor sites. Investigations of endocrine relationships are also underway, in terms of pineal-opiate interactions. The studies include both in vitro and in vivo preparations. The majority of the studies involve tissue obtained from rats, and no human studies are involved at this time.